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use std::io::{Result, Error, ErrorKind}; use std::convert::TryFrom; /// Read the next byte of the UTF-8 character out of the given byte iterator. /// The byte is returned as a `u32` for later shifting. /// Returns an `InvalidData` error if the byte is not part of a valid UTF-8 sequence. /// Returns an `UnexpectedEof` error if the input iterator returns `None`. fn next_byte<I: Iterator<Item=u8>>(iter: &mut I) -> Result<u32> { match iter.next() { Some(c) => { if c & 0xC0 == 0x80 { Ok((c & 0x3F) as u32) } else { Err(Error::new(ErrorKind::InvalidData, "invalid UTF-8 sequence.")) } }, None => Err(Error::new(ErrorKind::UnexpectedEof, "unexpected end of UTF-8 sequence.")) } } /// Read the next Unicode codepoint given its first byte. /// The first input byte is given as a `u32` for later shifting. /// Returns an `InvalidData` error the input iterator does not output a valid UTF-8 sequence. /// Returns an `UnexpectedEof` error if the input iterator returns `None` before the end of the /// UTF-8 character. fn raw_decode_from<I: Iterator<Item=u8>>(a: u32, iter: &mut I) -> Result<u32> { if a & 0x80 == 0x00 { Ok(a) } else if a & 0xE0 == 0xC0 { let b = next_byte(iter)?; Ok((a & 0x1F) << 6 | b) } else if a & 0xF0 == 0xE0 { let b = next_byte(iter)?; let c = next_byte(iter)?; Ok((a & 0x0F) << 12 | b << 6 | c) } else if a & 0xF8 == 0xF0 { let b = next_byte(iter)?; let c = next_byte(iter)?; let d = next_byte(iter)?; Ok((a & 0x07) << 18 | b << 12 | c << 6 | d) } else { Err(Error::new(ErrorKind::InvalidData, "invalid UTF-8 sequence.")) } } /// Read the next Unicode character given its first byte. /// Returns an `InvalidData` error the input iterator does not output a valid UTF-8 sequence. /// Returns an `UnexpectedEof` error if the input iterator returns `None` before the end of the /// UTF-8 character. fn decode_from<I: Iterator<Item=u8>>(a: u32, iter: &mut I) -> Result<char> { match char::try_from(raw_decode_from(a, iter)?) { Ok(c) => Ok(c), Err(_) => Err(Error::new(ErrorKind::InvalidData, "invalid UTF-8 sequence.")) } } /// Read the next Unicode character out of the given [`u8`](u8) iterator. /// /// Returns `None` is the input iterator directly outputs `None`. /// Returns an [`InvalidData`](std::io::ErrorKind::InvalidData) error the input iterator does not /// output a valid UTF-8 sequence. /// Returns an [`UnexpectedEof`](std::io::ErrorKind::UnexpectedEof) error if the input iterator /// returns `None` before the end of an UTF-8 character. pub fn decode<I: Iterator<Item=u8>>(iter: &mut I) -> Option<Result<char>> { match iter.next() { Some(a) => Some(decode_from(a as u32, iter)), None => None } } /// UTF-8 decoder iterator. /// /// Transform the given [`u8`](u8) iterator into a [`io::Result<char>`](std::io::Result) iterator. /// This iterator cannot be used to decode an [`io::Read`](std::io::Read) source, since the input /// iterator would be over [`io::Result<u8>`](std::io::Result) and not `u8`. However in this case /// you can use the [`UnsafeDecoder`](crate::UnsafeDecoder) iterator. /// /// ## Example /// The `Decoder` iterator can be used, for instance, to decode `u8` slices. /// ```[rust] /// let bytes = [72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100, 33]; /// /// let decoder = Decoder::new(bytes.iter().cloned()); /// /// let mut string = String::new(); /// for c in decoder { /// string.push(c?); /// } /// /// println!("{}", string); /// ``` /// /// ## Errors /// A call to [`next`](Iterator::next) returns an [`InvalidData`](std::io::ErrorKind::InvalidData) /// error if the input iterator does not output a valid UTF-8 sequence, or an /// [`UnexpectedEof`](std::io::ErrorKind::UnexpectedEof) if the stream ends before the end of a /// valid character. pub struct Decoder<R: Iterator<Item=u8>> { bytes: R } impl<R: Iterator<Item=u8>> Decoder<R> { /// Creates a new `Decoder` iterator from the given `u8` source iterator. pub fn new(source: R) -> Decoder<R> { Decoder { bytes: source } } } impl<R: Iterator<Item=u8>> Iterator for Decoder<R> { type Item = Result<char>; fn next(&mut self) -> Option<Result<char>> { decode(&mut self.bytes) } }